1. Field of the Invention
The invention relates to signal detectors and cameras having high sensitivity in the THz range, and more particularly, to high sensitivity THz signal detectors and cameras employing photonic crystal technology.
2. Description of the Related Art
The term “THz wave” refers to electromagnetic radiation with frequency in the range of 100 GHz-10 THz (which corresponds to a wavelength of 30 μm-3 mm). This frequency is located between microwave frequency and infrared frequency. Due to the absence of effective THz wave generation and detection methods, the knowledge about the performance of THz band electromagnetic radiation is limited. This gave rise to a “THz gap” in the electromagnetic spectrum.
With the rapid development of ultra-fast laser technology over the past several years, a stable and reliable way for generating THz pulse is provided. Thus, the study on THz wave radiation mechanism is promoted and the relevant detection and application technology flourish.
Compared with conventional light sources, the THz pulse light source has the following properties:
a) the THz wave has a pulse width of about 0.1-10 ps magnitude, which can be used not only for transient spectrum study with a subpicosecond time resolution, but also to avoid effectively the disturbance of background radiation noise with the assistance of sampling gate measurement technology. Currently, the signal to noise ratio for measuring THz wave radiation strength is greater than 104 level;
b) the THz pulse source usually comprises electromagnetic oscillation having more than one period; the bandwidth of a single pulse can cover the range of GHz to scores of THz;
c) the THz wave having a very high time and space coherence can be used as a camera light source, so that the amplitude and phase can be obtained at the same time; and
d) the THz wave has a photon energy only in the millielectronvolt range, so that the THz wave will not destroy a tested object, and thus can be used for non-destructive testing.
As a novel ultra-infrared coherent source, the THz wave is mainly applied in two technologies, namely, the THz wave time-domain spectrum analysis technology and the THz wave imaging technology. Potentially, it can also be applied for time resolution THz spectrum measurement for various solids, especially semiconductors, THz wave medical imaging, THz wave time-domain spectrum analysis of biological molecular conformation, null DNA molecule detection, THz wave micro-imaging, and so on.
The THz wave scanning delay system in conventional THz spectrum and imaging technology mainly adopts point-by-point mechanical scanning or electric translation scanning to realize time-delayed time domain spectrum measurement and imaging with the help of computer composition. This method has drawbacks such that an upper limit for scanning exists, the scanning speed is insufficient, the spectrum information cannot be observed timely, the time-space resolution is poor, and thus a real-time imaging is difficult to realize. Besides, the hot background noise, resulting from the slow scanning speed, cannot be suppressed effectively, which limits the practical application of the THz imaging technology. For example, for inspection at customs or safety checks at other confidential places, the image signal needs to be obtained immediately, leading to the requirement for developing practical THz detector and camera.
On the other hand, most current THz detection and imaging technologies are realized by means of electro-optical modulating cell, which also obstructs the integration of THz detector and camera.
Chinese Pat. Appl. No. CN 03116029.8 entitled “THz wave two-dimensional electro-optic area array imaging method” introduces a two-dimensional area array electro-optic crystal THz signal detector. Though the time-space resolution and signal-noise ratio are good and instant imaging can be realized, the detection sensitivity is not satisfactory and the capability to detect low power THz signal is poor.